The Origin and Shaping of Planetary Nebulae: Putting the Binary Hypothesis to the Test

TL;DR

This paper reviews the role of binary companions in shaping planetary nebulae, discussing theoretical models, observational challenges, and indirect tests to evaluate the binary hypothesis for nebula formation.

Contribution

It critically examines the binary hypothesis for planetary nebulae formation, highlighting observational obstacles and proposing indirect testing methods.

Findings

Binary companions likely influence nebula shapes

Observational tests face significant challenges

Indirect evidence supports the binary hypothesis

Abstract

Planetary nebulae (PNe) are circumstellar gas ejected during an intense mass-losing phase in the the lives of asymptotic giant branch stars. PNe have a stunning variety of shapes, most of which are not spherically symmetric. The debate over what makes and shapes the circumstellar gas of these evolved, intermediate mass stars has raged for two decades. Today the community is reaching a consensus that single stars cannot trivially manufacture PNe and impart to them non spherical shapes and that a binary companion, possibly even a sub-stellar one, might be needed in a majority of cases. This theoretical conjecture has however not been tested observationally. In this review we discuss the problem both from the theoretical and observational standpoints, explaining the obstacles that stand in the way of a clean observational test and ways to ameliorate the situation. We also discuss indirect tests of this hypothesis and its implications for stellar and galactic astrophysics.